1. Field of the Invention
This invention relates to a beam for use in a grid that supports panels and ceiling fixtures in a suspended ceiling. These fixtures include fluorescent light fixtures.
The beams used in such grid are generally of an inverted T-shape in cross-sections.
2. Background Information
Prior art beams used in grids in suspended ceilings are generally of inverted T-shape, with a bulb at the top, a vertical web extending downward from the bulb, and horizontal flanges at the bottom of the web. The height of the beam from the top of a flange to the top of the bulb, which is generally rectangular in cross-section is generally limited to 11/2". This beam height is so limited in order to accommodate the standard conventional fluorescent ceiling light fixture box frame.
The beams are generally formed from a flat strip of sheet metal by folding the strip along its longitudinal center.
These beams are subject to loads that tend to deflect the beams downward between beam support points, such as support wires. Such loads include acoustical panels as well as the above-mentioned lights and air diffusers. The beams must be strong enough to resist downward deflection from such loads within limits set by the controlling building codes.
In accordance with known beam design practice, the beam could be made stronger against downward deflection by increasing the web height, and/or by increasing the metal thickness from which the beam is formed. Since the web height has been set in the suspended ceiling industry at 11/2" to avoid interference with the standard fluorescent light box frame, the conventional way of strengthening the beam in the prior art was to use thicker metal, including reinforcement layers within, or on the bulb, as seen in U.S. Pat. Nos. Re. 31,528; 4,520,609 and 4,852,325. Such beam construction resulted in a costlier beam.